U.S. patent application number 11/009217 was filed with the patent office on 2006-06-15 for adapting short-wavelength led's for polychromatic, broadband, or "white" emission.
This patent application is currently assigned to 3M Innovative Properties Comapany. Invention is credited to Michael A. Haase, Thomas J. Miller, Terry L. Smith, Xiaoguang Sun.
Application Number | 20060124917 11/009217 |
Document ID | / |
Family ID | 35954099 |
Filed Date | 2006-06-15 |
United States Patent
Application |
20060124917 |
Kind Code |
A1 |
Miller; Thomas J. ; et
al. |
June 15, 2006 |
Adapting short-wavelength LED's for polychromatic, Broadband, or
"white" emission
Abstract
An adapted LED is provided comprising a short-wavelength LED and
a re-emitting semiconductor construction, wherein the re-emitting
semiconductor construction comprises at least one potential well
not located within a pn junction. The potential well(s) are
typically quantum well(s). The adapted LED may be a white or
near-white light LED. The re-emitting semiconductor construction
may additionally comprise absorbing layers surrounding or closely
or immediately adjacent to the potential well(s). In addition,
graphic display devices and illumination devices comprising the
adapted LED according to the present invention are provided.
Inventors: |
Miller; Thomas J.;
(Woodbury, MN) ; Haase; Michael A.; (Saint Paul,
MN) ; Smith; Terry L.; (Roseville, MN) ; Sun;
Xiaoguang; (Woodbury, MN) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Comapany
|
Family ID: |
35954099 |
Appl. No.: |
11/009217 |
Filed: |
December 9, 2004 |
Current U.S.
Class: |
257/13 ; 257/79;
257/94; 257/95 |
Current CPC
Class: |
H01L 2224/0508 20130101;
H01L 24/05 20130101; H01L 2924/13091 20130101; H01L 2224/05568
20130101; H01L 2224/05023 20130101; H01L 2924/13055 20130101; H01L
2224/05001 20130101; H01L 33/08 20130101; H01L 2224/14 20130101;
H01L 2224/05541 20130101; H01L 2224/05005 20130101; H01L 2924/13055
20130101; H01L 2924/00 20130101; H01L 2924/13091 20130101; H01L
2924/00 20130101 |
Class at
Publication: |
257/013 ;
257/095; 257/094; 257/079 |
International
Class: |
H01L 29/06 20060101
H01L029/06; H01L 33/00 20060101 H01L033/00 |
Claims
1. An adapted LED comprising a short-wavelength LED and a
re-emitting semiconductor construction, wherein said re-emitting
semiconductor construction comprises a potential well not located
within a pn junction.
2. The adapted LED according to claim 1 wherein said re-emitting
semiconductor construction additionally comprises an absorbing
layer closely adjacent to at least one of said at least one
potential well.
3. The adapted LED according to claim 1 wherein said re-emitting
semiconductor construction additionally comprises an absorbing
layer immediately adjacent to at least one of said at least one
potential well.
4. The adapted LED according to claim 1 wherein said re-emitting
semiconductor construction comprises at least one first potential
well not located within a pn junction having a first transition
energy and at least one second potential well not located within a
pn junction having a second transition energy not equal to said
first transition energy.
5. The adapted LED according to claim 1 wherein said
short-wavelength LED is a UV LED.
6. The adapted LED according to claim 1 wherein said
short-wavelength LED is a green, blue or violet LED.
7. The adapted LED according to claim 1 wherein said
short-wavelength LED is a blue LED.
8. The adapted LED according to claim 5, wherein said re-emitting
semiconductor construction comprises at least one first potential
well not located within a pn junction having a first transition
energy corresponding to blue-wavelength light, at least one second
potential well not located within a pn junction having a second
transition energy corresponding to green-wavelength light, and at
least one third potential well not located within a pn junction
having a third transition energy corresponding to red-wavelength
light.
9. The adapted LED according to claim 6, wherein said re-emitting
semiconductor construction comprises at least one first potential
well not located within a pn junction having a first transition
energy corresponding to yellow- or green-wavelength light and at
least one second potential well not located within a pn junction
having a second transition energy corresponding to orange- or
red-wavelength light.
10. The adapted LED according to claim 7, wherein said re-emitting
semiconductor construction comprises at least one first potential
well not located within a pn junction having a first transition
energy corresponding to yellow- or green-wavelength light and at
least one second potential well not located within a pn junction
having a second transition energy corresponding to orange- or
red-wavelength light.
11. The adapted LED according to claim 7, wherein said re-emitting
semiconductor construction comprises at least one first potential
well not located within a pn junction having a first transition
energy corresponding to green-wavelength light and at least one
second potential well not located within a pn junction having a
second transition energy corresponding to red-wavelength light.
12. The adapted LED according to claim 1 wherein said at least one
potential well includes a quantum well.
13. The adapted LED according to claim 2 wherein said at least one
potential well includes a quantum well.
14. The adapted LED according to claim 3 wherein said at least one
potential well includes a quantum well.
15. The adapted LED according to claim 4 wherein said at least one
first potential well includes a first quantum well and wherein said
at least one second potential well includes a second quantum
well.
16. The adapted LED according to claim 5 wherein said at least one
potential well includes a quantum well.
17. The adapted LED according to claim 6 wherein said at least one
potential well includes a quantum well.
18. The adapted LED according to claim 7 wherein said at least one
potential well includes a quantum well.
19. The adapted LED according to claim 8 wherein said at least one
first potential well includes a first quantum well, wherein said at
least one second potential well includes a second quantum well, and
wherein said at least one third potential well includes a third
quantum well.
20. The adapted LED according to claim 9 wherein said at least one
first potential well includes a first quantum well and wherein said
at least one second potential well includes a second quantum
well.
21. The adapted LED according to claim 10 wherein said at least one
first potential well includes a first quantum well and wherein said
at least one second potential well includes a second quantum
well.
22. The adapted LED according to claim 11 wherein said at least one
first potential well includes a first quantum well and wherein said
at least one second potential well includes a second quantum
well.
23. A graphic display device comprising the adapted LED according
to claim 1.
24. An illumination device comprising the adapted LED according to
claim 1.
25. A graphic display device comprising the adapted LED according
to claim 2.
26. An illumination device comprising the adapted LED according to
claim 2.
27. A graphic display device comprising the adapted LED according
to claim 6.
28. An illumination device comprising the adapted LED according to
claim 6.
29. A graphic display device comprising the adapted LED according
to claim 10.
30. An illumination device comprising the adapted LED according to
claim 10.
31. A graphic display device comprising the adapted LED according
to claim 12.
32. An illumination device comprising the adapted LED according to
claim 12.
33. A graphic display device comprising the adapted LED according
to claim 13.
34. An illumination device comprising the adapted LED according to
claim 13.
35. A graphic display device comprising the adapted LED according
to claim 17.
36. An illumination device comprising the adapted LED according to
claim 17.
37. A graphic display device comprising the adapted LED according
to claim 21.
38. An illumination device comprising the adapted LED according to
claim 21.
39. The adapted LED according to claim 7, wherein said re-emitting
semiconductor construction comprises at least one first potential
well not located within a pn junction having a first transition
energy corresponding to yellow-wavelength light.
40. The adapted LED according to claim 5, wherein said re-emitting
semiconductor construction comprises at least one first potential
well not located within a pn junction having a first transition
energy corresponding to blue-wavelength light and at least one
second potential well not located within a pn junction having a
second transition energy corresponding to yellow-wavelength
light.
41. The adapted LED according to claim 1, wherein said
short-wavelength LED comprises III-V semiconductors and said
re-emitting semiconductor construction comprises II-VI
semiconductors.
42. The adapted LED according to claim 1, wherein said
short-wavelength LED comprises GaN semiconductors and said
re-emitting semiconductor construction comprises II-VI
semiconductors.
Description
FIELD OF THE INVENTION
[0001] This invention relates to adaptation of short-wavelength
LED's to emit polychromatic or broadband light, which may appear as
white or near-white light, by addition of a re-emitting
semiconductor construction to down-convert a portion of the emitted
light to longer wavelengths.
BACKGROUND OF THE INVENTION
[0002] Light emitting diodes (LED's) are solid-state semiconductor
devices which emit light when an electrical current is passed
between anode and cathode. Conventional LED's contain a single pn
junction. The pn junction may include an intermediate undoped
region; this type of pn junction may also be called a pin junction.
Like non-light emitting semiconductor diodes, conventional LED's
pass an electrical current much more readily in one direction,
i.e., in the direction where electrons are moving from the n-region
to the p-region. When a current passes in the "forward" direction
through the LED, electrons from the n-region recombine with holes
from the p-region, generating photons of light. The light emitted
by a conventional LED is monochromatic in appearance; that is, it
is generated in a single narrow band of wavelengths. The wavelength
of the emitted light corresponds to the energy associated with
electron-hole pair recombination. In the simplest case, that energy
is approximately the band gap energy of the semiconductor in which
the recombination occurs.
[0003] Conventional LED's may additionally contain one or more
quantum wells at the pn junction which capture high concentrations
of both electrons and holes, thereby enhancing light-producing
recombination. Several investigators have attempted to produce an
LED device which emits white light, or light which appears white to
the 3-color perception of the human eye.
[0004] Some investigators report the purported design or
manufacture of LED's having multiple quantum wells within the pn
junction, where the multiple quantum wells are intended to emit
light at different wavelengths. The following references may be
relevant to such a technology: U.S. Pat. No. 5,851,905; U.S. Pat.
No. 6,303,404; U.S. Pat. No. 6,504,171; U.S. Pat. No. 6,734,467;
Damilano et al., Monolithic White Light Emitting Diodes Based on
InGaN/GaN Multiple-Quantum Wells, Jpn. J. Appl. Phys. Vol. 40
(2001) pp. L918-L920; Yamada et al., Phosphor Free
High-Luminous-Efficiency White Light-Emitting Diodes Composed of
InGaN Multi-Quantum Well, Jpn. J. Appl. Phys. Vol. 41 (2002) pp.
L246-L248; Dalmasso et al., Injection Dependence of the
Electroluminescence Spectra of Phosphor Free GaN-Based White Light
Emitting Diodes, phys. stat. sol. (a) 192, No. 1, 139-143
(2003).
[0005] Some investigators report the purported design or
manufacture of LED devices which combine two conventional LED's,
intended to independently emit light at different wavelengths, in a
single device. The following references may be relevant to such a
technology: U.S. Pat. No. 5,851,905; U.S. Pat. No. 6,734,467; U.S.
Pat. Pub. No. 2002/0041148 A1; U.S. Pat. Pub. No. 2002/0134989 A1;
and Luo et al., Patterned three-color ZnCdSe/ZnCdMgSe quantum-well
structures for integrated full-color and white light emitters, App.
Phys. Letters, vol. 77, no. 26, pp. 4259-4261 (2000).
[0006] Some investigators report the purported design or
manufacture of LED devices which combine a conventional LED element
with a chemical phosphor, such as yttrium aluminum garnet (YAG),
which is intended to absorb a portion of the light emitted by the
LED element and re-emit light of a longer wavelength. U.S. Pat. No.
5,998,925 and U.S. Pat. No. 6,734,467 may be relevant to such a
technology.
[0007] Some investigators report the purported design or
manufacture of LED's grown on a ZnSe substrate n-doped. with I, Al,
Cl, Br, Ga or In so as to create fluorescing centers in the
substrate, which are intended to absorb a portion of the light
emitted by the LED element and re-emit light of a longer
wavelength. U.S. Pat. App. No. 6,337,536 and Japanese Pat. App.
Pub. No. 2004-072047 may be relevant to such a technology.
SUMMARY OF THE INVENTION
[0008] Briefly, the present invention provides an adapted LED
comprising a short-wavelength LED and a re-emitting semiconductor
construction, wherein the re-emitting semiconductor construction
comprises at least one potential well not located within a pn
junction. The potential well(s) are typically quantum well(s). In
one embodiment, the re-emitting semiconductor construction
additionally comprises an absorbing layer closely or immediately
adjacent to a potential well. In one embodiment, the re-emitting
semiconductor construction additionally comprises at least one
second potential well not located within a pn junction having a
second transition energy not equal to the transition energy of the
first potential well. In one embodiment, the short-wavelength LED
is a UV LED. In one such embodiment, the re-emitting semiconductor
construction comprises at least one first potential well not
located within a pn junction having a first transition energy
corresponding to blue-wavelength light, at least one second
potential well not located within a pn junction having a second
transition energy corresponding to green-wavelength light, and at
least one third potential well not located within a pn junction
having a third transition energy corresponding to red-wavelength
light. In one embodiment, the short-wavelength LED is a visible
light LED, typically a green, blue or violet LED, more typically a
green or blue LED, and most typically a blue LED. In one such
embodiment, the re-emitting semiconductor construction comprises at
least one first potential well not located within a pn junction
having a first transition energy corresponding to yellow- or
green-wavelength light, more typically green-wavelength light, and
at least one second potential well not located within a pn junction
having a second transition energy corresponding to orange- or
red-wavelength light, more typically red-wavelength light.
[0009] In another aspect, the present invention provides a graphic
display device comprising the adapted LED according to the present
invention.
[0010] In another aspect, the present invention provides an
illumination device comprising the adapted LED according to the
present invention.
[0011] In this application:
[0012] with regard to a stack of layers in a semiconductor device,
"immediately adjacent" means next in sequence without intervening
layers, "closely adjacent" means next in sequence with one or a few
intervening layers, and "surrounding" means both before and after
in sequence;
[0013] "potential well" means a layer of semiconductor in a
semiconductor device which has a lower conduction band energy than
surrounding layers or a higher valence band energy than surrounding
layers, or both;
[0014] "quantum well" means a potential well which is sufficiently
thin that quantization effects raise the electron-hole pair
transition energy in the well, typically having a thickness of 100
mm or less;
[0015] "transition energy" means electron-hole recombination
energy;
[0016] "lattice-matched" means, with reference to two crystalline
materials, such as an epitaxial film on a substrate, that each
material taken in isolation has a lattice constant, and that these
lattice constants are substantially equal, typically not more than
0.2% different from each other, more typically not more than 0.1%
different from each other, and most typically not more than 0.01%
different from each other; and
[0017] "pseudomorphic" means, with reference to a first crystalline
layer of given thickness and a second crystalline layer, such as an
epitaxial film and a substrate, that each layer taken in isolation
has a lattice constant, and that these lattice constants are
sufficiently similar so that the first layer, in the given
thickness, can adopt the lattice spacing of the second layer in the
plane of the layer substantially without misfit defects.
[0018] It should be understood that, for any embodiment of the
present invention described herein comprising n-doped and p-doped
semiconductor regions, a further embodiment should be considered as
disclosed herein wherein n doping is exchanged with p doping and
vice-versa.
[0019] It should be understood that, where each of "potential
well," "first potential well," "second potential well" and "third
potential well" are recited herein, a single potential well may be
provided or multiple potential wells, which typically share similar
properties, may be provided. Likewise, it should be understood
that, where each of "quantum well," "first quantum well," "second
quantum well" and "third quantum well" are recited herein, a single
quantum well may be provided or multiple quantum wells, which
typically share similar properties, may be provided.
[0020] It is an advantage of certain embodiments of the present
invention to provide an LED device capable of emitting
polychromatic, white or near-white light.
BRIEF DESCRIPTION OF THE DRAWING
[0021] FIG. 1 is a schematic diagram of an LED according to one
embodiment of the present invention.
[0022] FIG. 2 is a flat-band diagram of conduction and valence
bands of semiconductors in a construction according to one
embodiment of the present invention. Layer thickness is not
represented to scale.
[0023] FIG. 3 is a graph indicating lattice constant and band gap
energy for a variety of II-VI binary compounds and alloys
thereof.
[0024] FIG. 4 is a graph representing the spectrum of light that
emits from a device according to one embodiment of the present
invention.
DETAILED DESCRIPTION
[0025] The present invention provides an adapted LED comprising a
short-wavelength LED and a re-emitting semiconductor construction,
wherein the re-emitting semiconductor construction comprises at
least one potential well not located within a pn junction. The
potential wells are typically quantum wells. In typical operation,
the short-wavelength LED emits photons in response to an electric
current and the re-emitting semiconductor construction emits
photons in response to the absorption of a portion of the photons
emitted from the short-wavelength LED. In one embodiment, the
re-emitting semiconductor construction additionally comprises an
absorbing layer closely or immediately adjacent to the potential
well. Absorbing layers typically have a band gap energy which is
less than or equal to the energy of photons emitted by the
short-wavelength LED and greater than the transition energy of the
potential wells of the re-emitting semiconductor construction. In
typical operation the absorbing layers assist absorption of photons
emitted from the short-wavelength LED. In one embodiment, the
re-emitting semiconductor construction additionally comprises at
least one second potential well not located within a pn junction
having a second transition energy not equal to the transition
energy of the first potential well. In one embodiment, the
short-wavelength LED is a UV LED. In one such embodiment, the
re-emitting semiconductor construction comprises at least one first
potential well not located within a pn junction having a first
transition energy corresponding to blue-wavelength light, at least
one second potential well not located within a pn junction having a
second transition energy corresponding to green-wavelength light,
and at least one third potential well not located within a pn
junction having a third transition energy corresponding to
red-wavelength light. In one embodiment, the short-wavelength LED
is a visible light LED, typically a green, blue or violet LED, more
typically a green or blue LED, and most typically a blue LED. In
one such embodiment, the re-emitting semiconductor construction
comprises at least one first potential well not located within a pn
junction having a first transition energy corresponding to yellow-
or green-wavelength light, more typically green-wavelength light,
and at least one second potential well not located within a pn
junction having a second transition energy corresponding to orange-
or red-wavelength light, more typically red-wavelength light. The
re-emitting semiconductor construction may comprise additional
potential wells and additional absorbing layers.
[0026] The adapted LED according to the present invention may be
composed of any suitable semiconductors, including Group IV
elements such as Si or Ge (other than in light-emitting layers),
III-V compounds such as InAs, AlAs, GaAs, InP, AlP, GaP, InSb,
AlSb, GaSb, and alloys thereof, II-VI compounds such as ZnSe, CdSe,
BeSe, MgSe, ZnTe, CdTe, BeTe, MgTe, ZnS, CdS, BeS, MgS and alloys
thereof, or alloys of any of the above. Where appropriate, the
semiconductors may be n-doped or p-doped by any suitable method or
by inclusion of any suitable dopant. In one typical embodiment, the
short wavelength LED is a III-V semiconductor device and the
re-emitting semiconductor construction is a II-VI semiconductor
device.
[0027] In one embodiment of the present invention, the compositions
of the various layers of the components of the adapted LED are
selected in light of the following considerations. Each layer
typically will be pseudomorphic to the substrate at the thickness
given for that layer or lattice matched to the substrate.
Alternately, each layer may be pseudomorphic or lattice matched to
immediately adjacent layers. Potential well layer materials and
thicknesses are typically chosen so as to provide a desired
transition energy, which will correspond to the wavelength of light
to be emitted from the quantum well. For example, the points
labeled 460 nm, 540 nm and 630 nm in FIG. 3 represent Cd(Mg)ZnSe
alloys having lattice constants close to that for an InP substrate
(5.8687 Angstroms or 0.58687 nm) and band gap energies
corresponding to wavelengths of 460 nm (blue), 540 nm (green) and
630 nm (red). Where a potential well layer is sufficiently thin
that quantization raises the transition energy above the bulk band
gap energy in the well, the potential well may be regarded as a
quantum well. The thickness of each quantum well layer will
determine the amount of quantization energy in the quantum well,
which is added to the bulk band gap energy to determine the
transition energy in the quantum well. Thus, the wavelength
associated with each quantum well can be tuned by adjustment of the
quantum well layer thickness. Typically thicknesses for quantum
well layers are between 1 nm and 100 nm, more typically between 2
nm and 35 nm. Typically the quantization energy translates into a
reduction in wavelength of 20 to 50 nm relative to that expected on
the basis of the band gap energy alone. Strain in the emitting
layer may also change the transition energy for potential wells and
quantum wells, including the strain resulting from the imperfect
match of lattice constants between pseudomorphic layers.
[0028] Techniques for calculating the transition energy of a
strained or unstrained potential well or quantum well are known in
the art, e.g., in Herbert Kroemer, Quantum Mechanics for
Engineering, Materials Science and Applied Physics (Prentice Hall,
Englewood Cliffs, N.J., 1994) at pp. 54-63; and Zory, ed., Quantum
Well Lasers (Academic Press, San Diego, Calif., 1993) at pp. 72-79;
both incorporated herein by reference.
[0029] Any suitable emission wavelengths may be chosen, including
those in the infrared, visible, and ultraviolet bands. In one
embodiment of the present invention, the emission wavelengths are
chosen so that the combined output of light emitted by the adapted
LED creates the appearance of any color that can be generated by
the combination of two, three or more monochromatic light sources,
including white or near-white colors, pastel colors, magenta, cyan,
and the like. In another embodiment, the adapted LED according to
the present invention emits light at an invisible infrared or
ultraviolet wavelength and at a visible wavelength as an indication
that the device is in operation. Typically the short-wavelength LED
emits photons of the shortest wavelength, so that photons emitted
from the short-wavelength LED have sufficient energy to drive the
potential wells in the re-emitting semiconductor construction.
[0030] FIG. 1 is a schematic diagram of an adapted LED according to
one embodiment of the present invention. Adapted LED 50 includes
short-wavelength LED 20 and re-emitting semiconductor construction
10. Re-emitting semiconductor construction 10 may be attached to
the emitting surface of short-wavelength LED 20 by any suitable
method, including the use of adhesive or welding materials,
pressure, heat or combinations thereof. In the depicted embodiment,
adapted LED 50 is flip-chip mounted on header 40. Solder contacts
27 and 28 maintain electrical contact between LED electrodes 25 and
26 and header traces 42 and 43, respectively. Short-wavelength LED
20 is typically a UV wavelength LED or a visible wavelength LED.
Where short-wavelength LED 20 is a visible wavelength LED, it
typically a green, blue or violet wavelength LED and most typically
a blue or violet wavelength LED. Short-wavelength LED 20 may
comprise any suitable components. In the depicted embodiment,
short-wavelength LED 20 comprises electrical contacts 25 and 26, a
transparent base layer 21, and functional layers 22, 23 and 24.
Functional layers 22, 23 and 24 may represent any suitable LED
construction but typically represent a pn junction, including p-
and n-doped semiconductors 22 and 24 and a light-emitting region 23
which may comprise one or more quantum wells. A re-emitting
semiconductor construction 10 according to the present invention is
mounted on the emitting surface of the short-wavelength LED 20. In
the depicted embodiment, re-emitting semiconductor construction 10
comprises red quantum well layer 12, green quantum well layer 14,
and intermediate layers 11, 13 and 15. In one embodiment of the
present invention, intermediate layers 11, 13 and 15 include
support layers and absorbing layers, as described below. In one
typical embodiment, short wavelength LED 20 is a III-V
semiconductor device, such as a blue-emitting GaN-based LED, and
re-emitting semiconductor construction 10 is a II-VI semiconductor
device.
[0031] FIG. 2 is a band diagram representing conduction and valence
bands of semiconductors in a re-emitting semiconductor construction
according to one embodiment of the present invention. Layer
thickness is not represented to scale. Table I indicates the
composition of layers 1-9 in this embodiment and the band gap
energy (E.sub.g) for that composition. This construction may be
grown on an InP substrate. TABLE-US-00001 TABLE I Layer Composition
Band gap Energy (E.sub.g) 1 Cd.sub.0.24Mg.sub.0.43Zn.sub.0.33Se 2.9
eV 2 Cd.sub.0.35Mg.sub.0.27Zn.sub.0.38Se 2.6 eV 3
Cd.sub.0.70Zn.sub.0.30Se 1.9 eV 4
Cd.sub.0.35Mg.sub.0.27Zn.sub.0.38Se 2.6 eV 5
Cd.sub.0.24Mg.sub.0.43Zn.sub.0.33Se 2.9 eV 6
Cd.sub.0.35Mg.sub.0.27Zn.sub.0.38Se 2.6 eV 7
Cd.sub.0.33Zn.sub.0.67Se 2.3 eV 8
Cd.sub.0.35Mg.sub.0.27Zn.sub.0.38Se 2.6 eV 9
Cd.sub.0.24Mg.sub.0.43Zn.sub.0.33Se 2.9 eV
[0032] Layer 3 represents a single potential well which is a
red-emitting quantum well having a thickness of about 10 nm. Layer
7 represents a single potential well which is a green-emitting
quantum well having a thickness of about 10 nm. Layers 2, 4, 6 and
8 represent absorbing layers, each having a thickness of about 1000
nm. Layers 1, 5 and 9 represent support layers. Support layers are
typically chosen so as to be substantially transparent to light
emitted from quantum wells 3 and 7 and from short-wavelength LED
20. Alternately, the device may comprise multiple red- or
green-emitting potential wells or quantum wells separated by
absorbing layers and/or support layers.
[0033] Without wishing to be bound by theory, it is believed that
the embodiment of the present invention depicted in FIG. 1 operates
according to the following principles: When an electrical current
passes between electrodes 25 and 26, short-wavelength photons are
emitted from short-wavelength LED 20. Photons traveling in the
direction of the emitting surface of short-wavelength LED 20 enter
re-emitting semiconductor construction 10. Photons passing through
re-emitting semiconductor construction 10 may be absorbed and
re-emitted from the green-emitting quantum well 7 as
green-wavelength photons or from the red-emitting quantum well 3 as
red-wavelength photons. The absorption of a short-wavelength photon
generates an electron-hole pair which may then recombine in the
quantum wells, with the emission of a photon. The polychromatic
combination of blue-, green- and red-wavelength light emitted from
the device may appear white or near-white in color. The intensity
of blue-, green- and red-wavelength light emitted from the device
may be balanced in any suitable manner, including manipulation of
the number of quantum wells of each type, the use of filters or
reflective layers, and manipulation of the thickness and
composition of absorbing layers. FIG. 4 represents a spectrum of
light that emits from one embodiment of the device according to the
present invention.
[0034] Again with reference to the embodiment represented by FIG.
2, absorbing layers 2, 4, 5 and 8 may be adapted to absorb photons
emitted from short wavelength LED 20 by selecting a band gap energy
for the absorbing layers that is intermediate between the energy of
photons emitted from short wavelength LED 20 and the transition
energies of quantum wells 3 and 7. Electron-hole pairs generated by
absorption of photons in the absorbing layers 2, 4, 6 and 8 are
typically captured by the quantum wells 3 and 7 before recombining
with concomitant emission of a photon. Absorbing layers may
optionally have a gradient in composition over all or a portion of
their thickness, so as to funnel or direct electrons and/or holes
toward potential wells.
[0035] Where the short-wavelength LED 20 is a visible wavelength
LED, layers 11-15 of re-emitting semiconductor construction 10 may
be partially transparent to the light emitted from the short
wavelength LED. Vector B represents a blue wavelength photon
passing through re-emitting semiconductor construction 10. Vector R
represents a red wavelength photon emitted from red quantum well
layer 12 after absorption of a blue wavelength photon emitted from
short-wavelength LED 20. Vector G represents a green wavelength
photon emitted from green quantum well layer 14 after absorption of
a blue wavelength photon emitted from short-wavelength LED 20.
Alternately, where short-wavelength LED 20 is a UV wavelength LED,
layers 11-15 of re-emitting semiconductor construction 10 may block
a greater portion or substantially or completely all of the light
emitted from the short wavelength LED 20, so that a greater portion
or substantially or completely all of the light emitted from the
adapted LED 50 is light re-emitted from re-emitting semiconductor
construction 10. Where short-wavelength LED 20 is a UV wavelength
LED, re-emitting semiconductor construction 10 may include red-,
green- and blue-emitting quantum wells.
[0036] The adapted LED according to the present invention may
comprise additional layers of conducting, semiconducting or
non-conducting materials. Electrical contact layers may be added to
provide a path for supply of electrical current to the
short-wavelength LED. Electrical contact layers may be placed such
that the current passes also through the re-emitting semiconductor
construction, or such that the current does not pass through the
re-emitting semiconductor construction. Light filtering layers may
be added to alter or correct the balance of light wavelengths in
the light emitted by the adapted LED. To improve brightness and
efficiency, layers comprising a mirror or reflector may be
added.
[0037] In one embodiment, the adapted LED according to the present
invention is a white or near-white LED which emits light at four
principal wavelengths in the blue, green, yellow and red bands. In
one embodiment, the adapted LED according to the present invention
is a white or near-white LED which emits light at two principal
wavelengths in the blue and yellow bands.
[0038] The adapted LED according to the present invention may
comprise additional semiconductor elements comprising active or
passive components such as resistors, diodes, zener diodes,
conventional LED's, capacitors, transistors, bipolar transistors,
FET transistors, MOSFET transistors, insulated gate bipolar
transistors, phototransistors, photodetectors, SCR's, thyristors,
triacs, voltage regulators, and other circuit elements. The adapted
LED according to the present invention may comprise an integrated
circuit. The adapted LED according to the present invention may
comprise a display panel or an illumination panel.
[0039] The short-wavelength LED and the re-emitting semiconductor
construction which make up the adapted LED according to the present
invention may be manufactured by any suitable method, which may
include molecular beam epitaxy (MBE), chemical vapor deposition,
liquid phase epitaxy and vapor phase epitaxy. The elements of the
adapted LED according to the present invention may include a
substrate. Any suitable substrate may be used in the practice of
the present invention. Typical substrate materials include Si, Ge,
GaAs, IP, sapphire, SiC and ZnSe. The substrate may be n-doped,
p-doped, or semi-insulating, which may be achieved by any suitable
method or by inclusion of any suitable dopant. Alternately, the
elements of the adapted LED according to the present invention may
be without a substrate. In one embodiment, elements of the adapted
LED according to the present invention may be formed on a substrate
and then separated from the substrate. The elements of the adapted
LED according to the present invention may be joined together by
any suitable method, including the use of adhesive or welding
materials, pressure, heat or combinations thereof. In one
embodiment, the re-emitting semiconductor construction is formed on
a substrate, bonded to the short-wavelength LED, and then its
substrate is removed by physical, chemical or energetic methods.
Typically, the bond created is transparent. Bonding methods may
include interfacial or edge bonding. Optionally, refractive index
matching layers or interstitial spaces may be included.
[0040] The adapted LED according to the present invention may be a
component or the critical component of a graphic display device
such as a large- or small-screen video monitor, computer monitor or
display, television, telephone device or telephone device display,
personal digital assistant or personal digital assistant display,
pager or pager display, calculator or calculator display, game or
game display, toy or toy display, large or small appliance or large
or small appliance display, automotive dashboard or automotive
dashboard display, automotive interior or automotive interior
display, marine dashboard or marine dashboard display, marine
interior or marine interior display, aeronautic dashboard or
aeronautic dashboard display, aeronautic interior or aeronautic
interior display, traffic control device or traffic control device
display, advertising display, advertising sign, or the like.
[0041] The adapted LED according to the present invention may be a
component or the critical component of a liquid crystal display
(LCD), or like display, as a backlight to that display. In one
embodiment, the semiconductor device according to the present
invention is specially adapted for use a backlight for a liquid
crystal display by matching the colors emitted by the semiconductor
device according to the present invention to the color filters of
the LCD display.
[0042] The adapted LED according to the present invention may be a
component or the critical component of an illumination device such
as a free-standing or built-in lighting fixture or lamp, landscape
or architectural illumination fixture, hand-held or vehicle-mounted
lamp, automotive headlight or taillight, automotive interior
illumination fixture, automotive or non-automotive signaling
device, road illumination device, traffic control signaling device,
marine lamp or signaling device or interior illumination fixture,
aeronautic lamp or signaling device or interior illumination
fixture, large or small appliance or large or small appliance lamp,
or the like; or any device or component used as a source of
infrared, visible, or ultraviolet radiation.
[0043] Various modifications and alterations of this invention will
become apparent to those skilled in the art without departing from
the scope and principles of this invention, and it should be
understood that this invention is not to be unduly limited to the
illustrative embodiments set forth hereinabove.
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